1)A laser-spectroscopic system for elementary reaction level analysis of low temperature oxidation has been developed and applied to methoxymethyl + O2 reaction, which is the initial step of dimethyl ether oxidation. The system consists of near-IR multi-pass absorption optics for detection of HO2 and OH, UV absorption optics for detection of alkyl radical and alkyl peroxy radicals, and laser pulse photolysis to initiate the subject reaction. Time-resolved profiles of HO2, OH and methoxymethyl-peroxy radical were measured and compared to those calculated with kinetic models. Thermal decomposition of methoxymethyl radical was separately measured as the rate was a cause of uncertainty in the models. It was proposed in this study that methoxymethyl + O2 undergoes not only recombination to O2 adducts but also direct formation of OH + formaldehydes. The secondary reaction of OH + formaldehyde was confirmed to be the main route to HO2 formation, but another route through direct formation of H
… MoreCO was also suggested.2)Chemical-mechanistic analyses of two-step autoignition process have been conducted in a single-cylinder piston engine. As the behaviors of transient species during the steps are crucial for the analysis, detection techniques for such species were developed and applied. (1)The time-resolved sampling technique through an electrically actuated valve was improved by adopting a direct mass-spectroscopic detection in a differentially pumped vacuum system. With a noble correction eliminating the contribution of initially sampled wall-boundary components, effective resolution of less than 1 ms was attained. It was confirmed that the transient species such as HCHO and H2O2 are formed in the first cool ignition stage and disappear in the final hot ignition. The amounts relative to the partial fuel consumption were also consistent with the recent model of dimethyl-ether oxidation. (2)The transient species of cool ignition were also measure in the exhaust within hot ignition suppressed conditions. Although the range of experimental conditions such as equivalence ratio is limited in this method, observable species is expanded and the accuracy are better by using mass spectrometer and FT-IR. The detection of formic acid and methyl formate in the cool ignition of dimethyl ether demonstrate the relative correctness of the 2000 version of Curran et al. detailed oxidation model compared to the 1998 version. Less